Select wooden backed chairs that have a high back. Sit in the chair first to make sure it ends above your shoulder blades. The back should have rounded or padded corners so they don't dig into your back. The seat should be at least 17 inches deep.
Remove the seat cushions, if there are any, so that you sit lower in the chair. This further prevents the top edge of the chair back from digging into your shoulders.
Tie a cushion against the back of the chair for added comfort. Place a small lower back support pillow where the seat meets the chair back if you need further back support.